I've completed the swich over 7 times now, and if all goes according to plan, will be working on number 8 after this weekend.
As with most things, I alwasy try and go from simple to hard:
1) Just thaw, heat with hair dryer and toss it in...about half the time this actually works.
1A) Pre-scent the room by thawing near the enclosure.
1B) Leave it in the enclosure over night.
2) Dangle from tongs with a little movement.
3) Full on Zombie Dance.
4) Scent with tuna juice.
5) Brain the rat.
6) A combo of any of the above tricks.